Thread: help with error

You never initialize your pointer "a" to anything. It has random data in it.

You need to test for EOF after the fgetc().

Todd

I initialized a*, but I'm still getting the same problem...

I'm trying to read a file of polynomials where the first number tells you how many polynomials are in the file. From there I have to add, multiply, and evaluate them, but I have a general idea on how to do that. At the moment, I'm having problems with creating the array of pointers to separate polynomials.

<ex>

Code:

3
26x^5 + 5x^2 + 323x^3 + 50x^2 + 14x
8x^3 + 11x^2 + 34x + 4
21x^6 + 3x^5 + 4x + 4

Code:

#define MAXPOLY 100
#define CHAR 1000
#define NAME 50

int main(void) {

	FILE *text;
	int number, exp, p, k, go;
	float coeff;
	char again = 'Y', newFile = 'Y', operation, ch;
	char fileName[NAME], *polynomial[MAXPOLY], charArray[MAXPOLY], *token, *a;
	struct poly *first = NULL, *sum, *multiply1, *multiply2, *newLink, *pointers;


	while(newFile == 'Y' || newFile == 'y') {
		printf("\nEnter the file where the polynomials are found: \n");
		fscanf(stdin, " %s", &fileName);
		text = fopen(fileName, "r");
/* If file failed to open, print error statement and ask for a different file. */
		if(text == NULL) {
			printf("Error involved in opening file. Cannot open %s\n", fileName);
			continue;
		}
		fscanf(text, " %d", &number);
/* Create an array of pointers. If error involved in allocating memory, terminate program. */
		pointers = calloc(number, sizeof(struct poly));
		if(pointers == NULL) {
			printf("Error involved in allocating space. Cannot complete task.");
			break;
		}

		a = &charArray[0];
		ch = fgetc(text);
		for(k = 0; k < number; k++) {
			for(p = 0; p < MAXPOLY ; p++) {
				ch = fgetc(text);
				*(a+p) = ch;
				if(ch == '\n') {
					break;
				}
			}
			if(k < number - 1) {
				polynomial[k] = a;
				a = calloc(1,MAXPOLY*sizeof(char));
				if(a == NULL) {
					printf("Error involved in allocating space. Cannot complete task.");
					exit(EXIT_FAILURE);
				}
			}
		}
	return 0;
}

For a prudent programming practice, consider modifying your FOR loop:

Code:

for(p = 0; p < MAXPOLY ; p++) {

Code:

for(p = 0; ; p++) {
				ch = fgetc(text);
				*(a+p) = ch;
				if(ch == '\n') {
					break;
				}

use fgets

No, fgets() needs to be told the MAXIMUM of the string you want to be able to read - and it will read at most that much, or it finds a newline, whcihever happens first.

--
Mats

Code:

	char *fileName[NAME], *polynomial[MAXPOLY], charArray[MAXPOLY], *token, *a;
	struct poly *first = NULL, *sum, *multiply1, *multiply2, *newLink, *pointers;


	while(newFile == 'Y' || newFile == 'y') {
		printf("\nEnter the file where the polynomials are found: \n");
		fscanf(stdin, " %s", fileName);

Don't you ever get warnings? You should.
You are defining an array of pointers and passing that to fscanf. Unfortunately, it won't warn here, but other places possibly.

Read up on pointers and memory:
http://cpwiki.sourceforge.net/A_pointer_on_pointers

Originally Posted by arrgh

ok, I've changed the filename array to an array of type char and inserted an &. After compiling, there are 0 errors and 0 warnings, but the program still stops at

No no no. If you read the above article correctly, you should know that when passing an array, the address is passed, so in essence, a pointer is passed. If you add &, then it will pass the address of the pointer instead, which won't do you any good.

It's better you use fgets instead, since the compiler can warn you if you do wrong then.

No, check the manual for fgets again.
It should be

Code:

fgets(buffer, sizeof(buffer), stdin)